Free rent does not shorten the lease
A concession period sits on top of the paying term, not inside it. Getting that one relationship wrong shortens every re-letting cycle in a model and quietly improves the return.
The relationship
When a lease is described as "five years with three months free", the tenant pays for sixty months and occupies for sixty-three. The free period is additional. It is not three of the sixty.
That sounds obvious written down. It is not obvious in a model, where the term is usually one field and the free rent is another, and nothing stops them being added the wrong way round.
What it costs when it is wrong
Take a suite re-let with three months of downtime, three months free and a sixty-month paying term. The full cycle is sixty-six months before the suite comes up again.
Model it as sixty and the suite re-lets six months early, every cycle, for the whole hold. On a ten-year model that is most of an extra letting — with its rent arriving sooner, and its costs already counted.
The error always runs the same way. A shorter cycle means income arrives earlier, so the return improves. Nobody catches a model that flatters.
The check
Ask the model what month the suite next becomes available. If the answer is the acquisition month plus the term, the free rent and the downtime are not in there.
In DealWise the cycle is downtime, then free rent, then the paying term, and the rent roll reports the availability date from the sum of the three. It is not an assumption you can set — it is derived from the lease.
Every figure above is asserted against the calculation engine in commission-example.test.ts — the same code a live deal runs.